chapter 6: chemical reactions. chemical equation represents a chemical change or reaction reactants ...
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Chapter 6: Chemical Reactions
Chemical Equation
• represents a chemical change or reaction
Reactants Products
Reactants – chemicals before the reactionProducts – substance formed in the reaction
5 signs of a chemical reaction
1. Color Change
5 signs of a chemical reaction
2. Precipitation of a Solid
5 signs of a chemical reaction
3. Energy Change – heat or light absorbed or released
5 signs of a chemical reaction
4. Odor Changes
5 signs of a chemical reaction
5. Gas Release
• Reactions can be described several ways:1. In a sentence
Copper reacts with chlorine to form copper (II) chloride.
2. In a word equationCopper + chlorine copper (II) chloride
3.Using formulasCu + Cl2 CuCl2
Symbols used in ReactionsSymbol Explanation
+ Used to separate two reactants or two products
Yields, separates reactants and products
(s), (l), (g) State of matter; Fe (s)
(aq) Aqueous solution – dissolved in water
Heat supplied to the rxn
Catalyst used (speeds up the rxn time)
Assignment 7
Write the word equations below as chemical equations and balance:
1. Zinc and lead (II) nitrate react to form zinc nitrate and lead.
2. Aluminum bromide and chlorine gas react to form aluminum chloride
and bromine gas.
Diatomic Elements
3. Sodium phosphate and calcium chloride react to form calcium
phosphate and sodium chloride.
In a chemical reaction
• Law of Conservation of Matter states that matter isn’t created or destroyed.
• The way atoms are joined is changed
Because of the LAW OF CONSERVATION OF MATTER, we have to BALANCE EQUATIONS!!!
To BALANCE AN EQUATION means to make sure that the NUMBER of atoms of each
element is the same in the reactants and in the products!
Balancing Rules:
1. You may change the coefficients to any number you want, but…
2. You may NEVER change a subscript.
A coefficient is a number written in front of the compound
Balancing example #1
C + O CO2
Balancing example #2
Zn + HCl H2 + ZnCl2
Balancing example #3
CuO + C Cu + CO2
Balancing example #4
O3 O2
Balancing example #5
Al + CuCl2 Cu + AlCl3
Balancing example #6
C + H2 C3H8
Balancing example #7
CF4 + Br2 CBr4 + F2
Balancing example #8
Hg2I2 + O2 Hg2O + I2
Balancing example #9
N2 + H2 NH3
Balancing example #10
KClO3 KCl + O2
Balancing example #11
H2 + O2 H2O
Balancing example #12
AlBr3 + K2SO4 KBr + Al2(SO4)3
5 Types of Chemical Reactions
1. Synthesis2. Decomposition3. Single Replacement (Displacement)4. Double Replacement (Displacement)5. Combustion
Synthesis Reaction
Synthesis reaction – 2 substances are combined to form a single product
A + B AB
+
Synthesis Examples
2Mg + O2 2MgOMagnesium and oxygen combine to form
magnesium oxide.
2H2 + O2 2H2OHydrogen and oxygen combine to form
dihydrogen monoxide (water)
Decomposition Reaction
Decomposition reaction – A single compound is broken down into 2 or more products.
AB A + B
+
Decomposition Examples
2NaCl(s) 2Na(s) + Cl2(g)
Sodium chloride (table salt) decomposes into sodium and chlorine gas.
CaCO3 CaO + CO2
Limestone (CaCO3 ) decomposes into lime (CaO) and carbon dioxide.
Decomposition Demo
• Decomposition of Hydrogen Peroxide with MnO2 as a catalyst
H2O2 O2 + H2O
Single Replacement Reaction
Single Replacement reaction – A single element takes the place of an element in a compound.
A + BC B + AC
+ +
Single Replacement Examples
Mg + BeO Be + MgOMagnesium replaces beryllium in beryllium
oxide to form magnesium oxide and beryllium.
2Na + 2HCl H2 + 2NaCl
Sodium replaces hydrogen in hydrochloric acid to yield hydrogen and sodium chloride.
Single Replacement Demo
• Magnesium reacting with Hydrochloric acid• Compared to Copper reacting with HCl
Double Replacement Reaction
Double Replacement reaction – Elements in 2 compounds switch places to form 2 new compounds.
AB + CD AD + CB
+ +
Double Replacement Examples
MgO + BeS MgS + BeOOxygen and sulfur switch places to form
magnesium sulfide and beryllium oxide.
Na2S + Zn(NO3)2 2Na(NO3) + ZnS
Sulfur and nitrate switch places to form sodium nitrate and zinc sulfide.
Double Replacement Demo
• A double replacement between barium chloride and potassium sulfate
• Potassium Iodide and lead (II) nitrate produces potassium nitrate and lead (II) iodide
Combustion Reaction
Combustion reaction – hydrocarbon (H and C) burn in oxygen to produce water and carbon dioxide. Heat is given off as energy.
CxHy + O2 H2O + CO2
Combustion Examples
CH4 + 2O2 2H2O + CO2
Methane burns in oxygen to produce water and carbon dioxide.
C12H22O11 + 12O2 11H2O + 12CO2
A sugar molecule burns in oxygen to produce water and carbon dioxide
Combustion Demo
• Burn sugar• Burn gasoline
Factors that affect reaction rates
• Temperature– Higher temperature faster reaction
• Concentration– Changing the amounts of reactants– High concentration means more particles per
volume• (3% H2O2 vs. 30% H2O2 )
• Surface Area – Reactions occur faster when there is more surface
area• Sugar cube vs. sugar packet dissolving
• Catalyst– Used to speed up a reaction without being used
up – Enzymes are examples of catalyst
Can you slow a reaction down?
• Inhibitor – a substance added to slow reactions down– Added to food products
Limiting Reactant
• The reactant that is used up first
Making a bicycle requires1 frame + 2 wheels 1 bicycle
If you have 100 frames and 120 wheels, howmany bicycles can you manufacture? What is the limiting reactant?